Verdigris, Distilled. Syn. Crystallised verdigris. This name is applied to the normal acetate of copper, which is prepared in the wine districts by dissolving ordinary verdigris, 1 part, in good distilled vinegar, 2 parts; the operation being performed in a copper vessel by the aid of a gentle heat and agitation; the solution is afterwards slowly evaporated until a pedicle begins to form on the surface, when it is transferred into glazed earthen pans (‘oulas’), in each of which are placed 2 or 3 cleft sticks, and it is then left in a warm apartment for 14 or 15 days to crystallise.
A spurious article is often prepared by adding a solution of sulphate of copper, 121⁄2 lbs. to a solution of sugar of lead, 19 lbs., or q. s.,
and filtering, evaporating, and crystallising the mixture.
There is an acetate of copper and lime which resembles distilled verdigris in colour. It was manufactured pretty extensively in Scotland some years ago, and fetched a high price, till Dr Ure published an analysis of it in the ‘Edin. Phil. Trans.’ It is much inferior for all uses in the arts.
Pure distilled verdigris is entirely soluble in water, and is not precipitated on the addition of sulphuric acid or of ammonia in excess.
Verdigris, English. Prep. Blue vitriol, 24 lbs.; white vitriol, 16 lbs.; sugar of lead, 12 lbs.; alum, 2 lbs. (all coarsely powdered); mix, and heat them in a pot over the fire until they unite into a mass. Sold by fraudulent dealers for foreign verdigris.
VER′DITER. Syn. Blue verditer, Refiner’s verditer; Cendres bleues, Fr. A blue pigment, obtained by adding chalk, whiting, or milk of lime, to a solution of copper in nitric acid; or, by triturating recently precipitated and still moist carbonate of oxide of copper with hydrate of lime.
Prep. A quantity of whiting or milk of lime is put into a tub, and upon this the solution of copper is poured; the mixture is stirred every day for some hours together, until the liquor loses its colour; it is then poured off, and more solution of copper added; this is repeated until the whiting or lime has acquired the proper colour; the whole is then washed with water, drained, spread on chalk stones, and dried in the sun.
Obs. The cupreous solution employed in the above process is made by neutralising the nitric solution obtained from the refiners of gold and silver, by heating it along with metallic copper. For the finer qualities of verditer the lime should be of the purest kind, and the cupreous precipitate should be carefully triturated with it, after it is nearly dry, by which a fine velvety appearance is produced. The ‘cendres bleues en pâtes’ of the French differ from the above mainly in a solution of chloride of copper being employed, and in the resulting green precipitate being turned blue by the action of carbonate of potassa. Verditer is made into crayons whilst moist, or dried into a powder, or it is used as a water colour in the moist state.
Verditer, Green. Syn. Bremen green. The process for refiner’s verditer frequently miscarries, and a green colour is produced instead of a blue one. It may also be obtained directly by omitting the ‘blueing up’ with carbonate of potassa, mentioned above.